Coupling system



March 2, 1937. w. LYoNs COUPLING SYSTEM Filed April 22. 1935 .N aw@ ATTORNEY.

Patented Mar.. 2, 193%l 2,012,619 coUPLlNG srs'rlm K Walter Lyons, Flushing, N. Y., asignar to Hazeltine Corporation, a corporation of Delaware Application April 22, 1935, Serial No. 17,712

This invention relates to coupling systems and particularly to methods of, and circuit arrangements for, adjusting the coupling between two tuned circuits so as to vary the width of the frequency band passed by the system.

While my invention is of general application, it is especially adapted for embodiment in one -or more of the selective circuits of superheterodyne radio receivers, for controlling the selectivity thereof. Optimum delity consistent with the avoidance of interference from stations operating on adjacent carrier frequencies and from static and other noise sources, is obtainable by adjustment of the band width of the selective circuits to provide the required selectivity according to the conditions of operation. For conditions of considerable interference, a minimum band width, giving maximum selectivity, is required, while with negligible interference present, the band width, and hence the delity, may be increased to the maximum. Intermediate conditions of operation may be accommodated by intermediate adjustments of the band width. Various arrangements embodying these principles have been heretofore developed .and are commonly referred to as expanding selector", abbreviated as X. P. 8.", systems. For detailed descriptions of certain particularly satisfactory receivers embodying such systems, reference may be had to a copending application of Daniel E. Hamett, Serial No. 747,044, illed October 5, 1934, for Control system and patented April 2l, 1936, as U. S. Patent No. 2,038,359; and a copending application of Harold A. Wheeler and Nelson P. Case, Serial No. 696,990, led November '7, 1933, for Radio receiver and patented December 10, 1935, as U. S. Patent No. 2,024,017.

Where two identically tuned circuits are reactively coupled, they constitute a selective network and the width of the frequency band passed thereby is dependent upon the mutual coupling therebetween so ythat the band width, or selectivity", can be adjusted by varying the mutual coupling between the circuits. The band i5 passed is u'sually symmetrically disposed rela.-

tive to the resonant frequency of the tuned circuits, and even if the circuits are additionally coupled by other reactive elements, or if inadvertently coupled as by stray capacitance, the 50 band width may still be controlled symmetrically relative to the resonant frequency by adjusting only the mutual reactive coupling, provided the self-reactance oi the network remains unaltered.

In attempts to adjust the band width of coupled tuned circuits symmetrically, it has been cus- 5 tomary to vary the relative positions of electromagnetically coupled coils of thetwo circuits to alter the mutual inductance therebetween. Various diillculties are occasioned by this practice, however, particularly detuning -of the circuits and 1o consequent unsymmetrical expansion. Such results may be occasioned by a modification of stray capacitive couplings, or altering of the inductance or distributed capacitance of the moved coil b y changing its proximity to surrounding metal parts. These undesirable effects are accentuated when the system is employed for selecting relatively narrow bands of comparatively high frequencies.

It is desirable, in the economical design of radio receivers, that standard transformers, which provide a xed coupling, may be used interchangeably in coupling systems with either ilxed or adjustable selectivity. 'Ihe modification of s uch standard transformers to provide for adjustable selectivity and the provision of mechanism for adjustment thereof involve considerable -expense and require considerable added space. Furthermore, a precise adjustment of the coupling of such transformers, as by moving one of the windings thereof relative to the other, is somewhat dimcult to accomplish due to the relatively narrow range of adjustment that is required.

An object of this invention is to provide an improved method of adjusting the coupling between two coupled tuned circuits to vary the width of the band of frequencies passed thereby, and to provide improved coupling systems adapted for use in connection with such method.

A` further object of the invention is to provide an improved method and an improved system of the character described, in which a certain amount of xed reactive coupling obtains between the circuits and the coupling is adjusted by auxiliary means without alteration of the self-reactances of the circuits or modifications of the xed coupling, and in which the band width is adjustable symmetrically relative to a xedv frequency. 1 50 A further object of the invention is to provide an improved coupling system embodying means for varying the coupling thereof, adapted for use in connection with a system of the character aforedescribed, whereby a standard transformer providing a fixed coupling may be employed, a minimum amount of space will be required,

and a precise adjustment of the coupling may be obtained with facility of operation.

Various other and further objects of and advantages achieved by this invention will be apparent from the description thereof hereinafter set forth.

The present invention provides two tuned circuits having a fixed reactive coupling means and an adjustable auxiliary reactive coupling means. The coupling of the main reactance means is maintained constant while that of the auxiliary means is adjusted so as to vary th total coupling between the two circuits without changing the self-reactances thereof. The band width is thus adjusted symmetrically relative to the frequency to which the circuits are tuned, and

' hence the selectivity of the system isV controlled yso without detuning the circuits.

While the invention contemplates employingv reactive coupling means which are either inductive or capacitive, a present approved embodiment of the invention, which is hereinafter described in detail by way of example,'utilizes an improved inductive coupling arrangement. In this embodiment `the fixed reactive coupling means is vprovided by windings of a standard transformer and the auxiliary adjustable reactive coupling means is provided by adjustably coupled auxiliary windings connected in series with the respective transformer windings at the low potential ends thereof. The auxiliary windings preferably have a self-reactance which is a small fraction of that of the main coupling windings. By this arrangement the self-reactance of the circuits is not changed and the tuningis unaffected by adjustment of the coupling. The auxiliary windings being connected to the low potential ends of the main windings, the connections therebetween will be at relatively low potentials so that adjacent electrical units of the system will not be materially affected by any stray coupling therewith, thus allowing the auxiliary windings to bev located at any convenient place even though remote from the main windings. Further,V the selectivity of the system can be controlled with relatively great precision, as the desired small amount of change in the total coupling of the circuits is effected by the adjustment of the coupling of the auxiliary windings over a relatively wide range. The arrangement is thusin the nature of a vernier.A In addition to these advantages, the arrangement Arequires a minimum amount of added space over that required by an ordinary fixed transformer.

In the accompanying drawing, Fig. 1 is a cir- -cuit diagram illustrating thepresent invention and Fig. 2 is a sectional view of an adjustable coupling device suitable for use in connection with the invention. y

Referring in detail to the diawing, the invention is here illustrated as employed in connection with a superheterodyne radio receiver, those parts of the receiver which are well knownand do not comprise any part of the present invention being indicated schematically.

The receiver comprises a radio-frequency amplifier having its input circuit connected with an antenna I0 and a ground II and its output circuit connected with a modulator-oscillator. The/'output circuit of the modulator-oscillator is connected to the input section of an intermediate-frequency amplifier including a tuned coupling system I3 embodying the invention. The coupling system I3 comprises a main transformer I3a, which includes a primary winding I2 and a secondary winding Il, and an adjustable auxiliary transformer I3b having primary and secondary windings I1 and I8 connected in series with the windings I2 and I4, respectively, between their low potential ends and ground, the connection to the winding I'I including a source of operating voltage for the modulatoroscillator, indicated as +B. Adjustably fixed condensers I6 are connected across the primary and secondary circuits of the coupling system, as illustrated. The output sectionof the lcoupling system is connected to the input circuit of a pentode amplifier tube I5. The output circuit of the amplifier tube may be connected directly to the input section of a detector or, in case additional stages of intermediate-frequency amplification-are desired, it may be connected to the input section of an additional adjustable coupling circuit I9, similar in all respects to the coupling circuit I3 just described.

Suitable shields 2|v and 22 are provided for the main transformers and the auxiliary transformers, respectively, of both systems I3 and I9. A source of voltage, indicated generally at 20, provides operating potentials andfspace current for the tube I5. The output section of the circuit I9 is connected to additional intermediate-frequency amplifier stages which are, ln turn, connected to a detector.' The detector is connected through an audio-frequency amplifier with a loudspeaker.

Neglecting for the moment the auxiliary coupling devices I3 of the coupling circuits, the system described above comprises a conventional superheterodyne receiver the operation of which is well understood in the art. so that a detailed explanation thereof is deemed unnecessary. In

brief, signals intercepted by the antenna are selected and amplified'in the radio-frequency amplificr and supplied to the modulator-oscillator where the signals are converted to an intermediate frequency in the usual manner. The output of the modulator-oscillator is delivered to the intermediate-frequency amplifier wherein the coupling arrangements serve to select the desired band of frequencies, as hereinafter further explained, and these frequencies are amplified and supplied to the detector. The detector produces the audio-frequencies of modulation and supplies them to the audio-frequency amplifier whereby they are amplified and supplied in the usual manner to the loudspeaker for reproduction.

With the present invention, the desired adjustment of the band width may be accomplished in a variety of ways. For instance, the main reactive coupling means may be fixed to effect the desired maximum coupling between the circuits and the auxiliary reactive coupling means arranged in opposing relation to the fixed coupling means so that, as the latter is' varied through its range from maximum to minimum, the total couplingvof the circuits will be increased from minimum to maximum.

As another instance, the main reactive coupling means may be ,fixed to provide a value of coupling reactance between the circuits intermediate the desired maximum and minimum values and the auxiliary means adjusted to inf imum coupling between the circuits and thel auxillary coupling means may be adjusted in aiding relation with the main coupling means so that increases and decreases of the coupling of the auxiliary means-will serve, respectively, to increase or decrease the total coupling between the circuits.

For any of the above arrangements, a transformer of any of the well-known 'standard commercial types may be employed for the main or iixed reactive coupling means.` The auxiliary transformer, including the windings I1 and I0, proportioned as described, may have any desired structural form but is preferably constructed as a separate unit, or adjustable coupling device, one example of which is illustrated in Fig. 2. According to this arrangement, the movable winding IB is mounted within the stationary winding I1 on a rotatable shaft 23, suitably journaled in bearings 24 provided in the shield or housing 22 and having an operating knob 25. The windings I1 and Ill are angularly related to the' shaft 23, so

that by rotating the shaft'23 by the knob 25 the winding I8 is adjustable between a position with its axis coincident with the axis of the winding I1,

providing a maximum amount of coupling, and a position with its axis perpendicular to the axis of the winding I1, effecting a minimum amount of coupling. By this construction the coupling between the windings I1 and I8 may be varied over a -relatively wide range. The adjustable auxiliary windings of both the arrangements I3 and I9 are preferably mechanically connected for unicontrol, as indicated at 20, to allowA simultaneous adjustment of the selectivity of the two coupling systems. The units or elements providing the auxiliary reactive coupling means and the means for effect-v ing the adjustment thereof may thus -be very small and inexpensive parts. Advantages of this arrangement include the possibility of placing the auxiliary coupling means in any convenient location, the saving of space, and the precise ad'- justments obtainable by virtue of the relatively wide mechanical range over which the auxiliary reactive means may be varied.

The improved method which is provided by this invention may, of course. be practiced with any desirable circuit arrangement in a coupling `system which includes a pair of tuned circuits with' main fixed reactive coupling means and additional or auxiliary reactive coupling means. The essential features of the method include maintaining the coupling between the main coupling means constant and varying the coupling between the auxiliary coupling means, preferably over a relatively wide range, -thereby to vary the total coupling between the two circuits over the desired range to provide the required symmetrical band width adjustment for controlling the selectivity of the system without detuning.

While my invention is of application to band selecting circuits generally and is not restricted to any particular design. highly satisfactory results have been obtained from a superheterodyne receiver embodying the present invention and using substantially the same arrangement as described in detail hereinabove, and illustrated in che drawing nl this embodiment, the coupling systems I3 and Il were designed as follows:

Main windings I2 and il-l" apart on form 1" Each coili. d. by long mounted in aluminum can 2" by 2'-' by 31/2"; 120 turns 7s No. 40 Litz S. S. C.

L-570 microhenrles (in air at 1000 cycles) Equivalent mutual .inductance-about 4 to 5 microhenries'.

Auxiliary windings-- Rotor I8-40 turns 7s No. l40 S. S.

Litz layer-wound on form i. d. by 1'3" long L-29.6 microhenries can at 1000 cycles) Stator I130 turns '7s No. 40 S. S. Litz layer-wound on form i. d. by 1%" long L-29 microhenries (in can at 1000 cycles) Maximum mutual inductance-1'7.2 microhenries.

While certain applications of the invention, utilizing both capacitive and inductive coupling arrangements, have been described or mentioned, and the details of one example of the invention have been set forth, it will be apparent that various other applications of the invention, as well as various changes and modifications with regard to the particular example disclosed in detail, may be resorted to without departing from the spirit of this invention, and it will be understood that all and any such applications,

changes and modifications are contemplated asY a part of this invention as defined in the appended claims.

What is claimed isp- 1. A band-pass selector system-comprising two tuned circuits having fixed reactive coupling means and means for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant frequencyof said b and comprising adjustable auxiliary reactive coupling means having a self-reactance which is equal to a small fraction of that of said iixed coupling'means, and means for continuously adjusting the coupling of said auxiliary means over a relatively wide range without affecting self-reactance of said circuits, to vary the total coupling of the circuits over a substantially lesser range.

2. A band-pass selector system comprising two tuned circuits having fixed reactive coupling means of a single type and means for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant frequency of said band comprising adjustable auxiliary reactive coupling means of the same type having self-reactance which is equal to a small fraction of that of said fixed coupling means, and means for adjusting the coupling of said auxiliary coupling means over a relatively wide range without affecting the self-reactances of said circuits, to vary the total coupling of the circuits over a substantially lesser range.

3. A band-pass selector system comprising two tuned circuits having reactive coupling means of only one type including flxed reactive coupling means effective to provide a predetermined minimum coupling reactance between said circuits and means for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant frequency of said band comprising adjustable auxiliary reactive coupling means in aiding relation to said fixed coupling means and having selfreactance which is equal to a small fraction of thatof said fixed coupling means, and means for adjusting the coupling of said auxiliary cou- 16 pling means over a relatively wide range, to vary the total coupling of the circuits over a substantially lesser range.

4. A band-pass selector system comprising two tuned circuits having reactive coupling means of only one type including xed reactance coupling means effective to provide a predetermined maximum coupling reactance between said circuits and means for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant frequency of said band comprising adjustable auxiliary reactive coupling means in opposing relation to said ilxed coupling 'means and having self-reactance which is equal to a small fraction of that of said fixed coupling means, and means for adjusting the coupling of said auxiliary cou- 'pling means over a relatively wide range, to vary the total coupling oi the circuits over a sub- 'stantially lesser range. i l Y 5. A band-pass selector system comprising two tunedcircuits having reactive coupling means of only one type including fixed reactive coupling means effective to provide a predetermined coupling reactance between said circuits of a value 40 intermediate desired maximum and' minimum values and means for adjusting the width of the band of frequencies passed by the system symmetrlcally relative to the mean resonant. frequencyof said band comprising adjustable re- 45 active coupling means having self-reactance which is equal to a small fraction of that of said fixed coupling means, and means Vfor adjusting the coupling of said auxiliary coupling means over a relatively wide range in either aiding or 50 opposing relation to said fixed coupling means, to vary the total coupling of the circuits over a substantially lesser'range.

6. A band-pass selector system comprising two tuned circuits having reactive coupling means of 55 only one type including fixed inductive coupling means and means for adjusting the width ofthe band of frequencies passed by the systexn sym- L metrically relative to the mean resonant frequency of said band comprising adjustable aux- 60 iliary inductive coupling means having self-inductance which is equal to a small fraction of that of said ilxed coupling means, and means for adjusting the coupling of said auxiliary coupling means over a relatively wide range without af- 65 fecting the self-reactances of said circuits,to

vary the total coupling of the circuits over a substantially lesser range.

7. A band-pass selector system having grounded connections and comprising two tuned circuits 70 having reactive coupling means of only one type including relatively fixed inductive coupling windings and means for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant fre- 75 quency of said band comprising auxiliary adjustable inductive coupling windings, respectively connected between terminals of said main windings and said grounded connections and having self-inductance which is equal to a small fraction of that of said fixed windings, and means for s adjusting the coupling of said auxiliary windings over a relatively wide range, to vary the total coupling of the circuits over a substantially lesser range.

8. A band-pass selector system comprising two l0 tuned circuits having reactive coupling means of only one type including ilxed inductive coupling l means effective to provide a predetermined mini-V mum coupling inductance between said circuits and means for adjusting the width of the band 16 of frequencies passed by the system symmetrically relative to the mean resonant frequency of said band comprising adjustable auxiliary inductive coupling means in aiding relation to said xed coupling means and having self-inductance which 20 is equal to a small fraction of that of said'ilxed coupling means, and means for adjusting the coupling of said auxiliary coupling means over a relatively wide range, to vary the total coupling of the circuits over a substantially lesser range.

9. In a superheterodyne radio receiver including means for converting a received radio-frequency signal, to an intermediate frequency, an intermediate-frequency selecting system comprising two tuned circuits having reactive coupling means of only one type including ilxed reactive coupling means and adjustable auxiliary reactivecoupling means, and means for adisting the coupling of said auxiliary coupling means over a relatively wide range without affecting the self-reactances oi' said circuits, to vary the total coupling of the circuits over a substantially lesser range.

10. In a wave-signaling system, a pair of bandpass selector systems, a vacuum tube amplifier interconnecting the output section of one selector 40 .system with the input section of the other, each of said selector systems comprising two tuned circuits having ilxed reactive coupling means and kmeans for adjusting the width of the band of frequencies passed by the system symmetrically relative to the mean resonant frequency of said band comprising adjustable auxiliary reactive, coupling means having a self-reactance which is equal to a small fraction of that of said ilxed coupling means, means for adjusting the coupling of said auxiliary means over a relatively wide range without affecting self-reactance o1' said circuits,

to vary` the total coupling of the circuits over a .suhstantially'lesser range, and unicontrol means for simultaneously actuating the coupling adjusting means of both of said selector systems;

y1l. Ina band-pass selector system comprising two tuned circuits having main reactive coupling means and auxiliary reactive coupling means of the same type having self-reactance which is equal to a small fraction of that o'f said main coupling means, the method of adjusting the width of the band of frequencies passed'by said system which comprises maintaining constant the coupling of said main coupling means and varying the coupling of said auxiliary coupling means over a relatively wide range without affecting the selfreactances of said circuits, to vary the total coupling of the circuits over a substantially lesser range.

l2. In a band-pass selector system comprising two tuned circuits having main reactive coupling means proportioned to provide a predetermined value of coupling and auxiliary reactive coupling means of the same type as and in aiding relation 75 aovao'ro 5 to said main coupling means and having self-reactance which is equal to a lsmall fraction of that of said main coupling means, the method of ad-` justing the width of the band of frequencies 5 passed by said `systexn from that provided by `said predetermined value of coupling to that provided by a .substantially greater value ot coupling, which comprises maintaining constant the CERTIFICATE 0F CORRECTION.

Patent No. 2,072,679.

March 2, 193?.

WALTER LYONS.

A It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 4,

second column, line 32, claim 9, after the word "and". insert the words means for adjusting the width 0f the band "of freqenoies passed by the system symmetrically relative to the mean -resonant frequency of said band comprising; and that the said Letters Patent should be read ywith this correction therein that the same may conformto the record of the case in the Patent Qffice.

signed 'endvsealed this 1st dayiof June, A, D. 1957.

(Seal) Henry Van Alrsdale Acting Commissioner of Patents,- 

